The present invention relates generally to dental implants, and more specifically to a dental implant having an improved coronal configuration to take advantage of the presenting bony topography that is often present immediately following tooth extraction prior to any healing or remodeling process. This ridge lap dental implant is suitable, but not limited to, both immediate and delayed implant placement in the upper anterior region of the mouth.
Dental implants are used in place of missing natural teeth to provide a base of support for single, multiple teeth or full arch prosthetics. These implants generally include two components, the implant itself and the prosthetic mounting component referred to as an abutment upon which the final prosthesis is installed. The implant has apical and coronal ends, whereby the coronal end accepts the base of the prosthetic abutment using connection mechanisms of different designs. One such mechanism is a deep female conical receptor with an internal alignment or anti-rotational element such as a hex, double hex, spline or other single/multi sided arrangement used for prosthetic alignment and anti-rotational stability. Deep female conical connections have been shown to be the most stable mechanisms by preventing micro movement between the implant body and the abutment under normal loading conditions. It has been suggested that preventing micro movement is one of the key factors required for crestal bone maintenance.
Dental implants are used in place of extracted (and/or missing) natural teeth as the base of support for an abutment and final prosthesis to restore normal oral function. But once a tooth is no longer present, the bone from which the tooth originated heals and is forever changed. Accordingly, while dental implants should be designed to take into account the healing process of bone after tooth loss, this is seldom the case. In fact, dental implant designs for the most part are not designed to take into consideration the presenting bony topography prior to implant placement. In fact, it is common for surgeons to modify or flatten the bone to suit the implant configuration rather than design the implant to suit the presenting anatomy.
In practice, the implant body is surgically inserted in the patients jaw and becomes integrated with the bone. This can be done immediately at the time of tooth extraction or in a delayed manner allowing healing and remodeling to occur first. More specifically, the implant body is screwed or pressed into holes drilled in the respective bone or the apical end of extraction socket is prepared to accept the insertion of a dental implant immediately. The surface of the implant body is characterized by macroscopic and microscopic features that aid in the process of osseointegration. Once the implant is fully integrated with the jaw bone or in some cases at the time of insertion the abutment is ready to be mounted. For two-stage implant designs, the abutment passes through the soft tissue that covers the coronal end of the implant after healing and acts as the mounting feature for the prosthetic device to be used to restore oral function. Implants of the single-stage design extend at least partially through the soft tissue at the time of surgical insertion. The coronal end of the single stage implant body acts as a built-in abutment with the margin of the coronal collar usually being employed as the margin of attachment for the prosthesis used to restore oral function. These components, the implant and abutment, are typically fabricated from titanium or titanium alloy as well as zirconia based, alumina based or sapphire based ceramics. In some instances, ceramics and metals are combined to make a single component, though this is usually limited to the abutment component of the implant system. Titanium zirconium alloys and in the future nano structure titanium could become used due to significant increased strength.
Implant designs have gone through a considerable amount of trial and error in an attempt to deal with the issue of the bone not healing evenly once a tooth has been extracted. It has been found that bone heals based on the principles of bone biology, surrounding bony and soft tissue anatomy, as well as blood supply to the area. To a certain degree, bone healing and/or remodeling is also influenced by the placement and subsequent loading of an implant fixture. Only a limited number of studies have been conducted regarding bone loss patterns following tooth loss. Two such studies, one by Pietrokovski and Massler, published in the Journal of Prosthetic Dentistry in 1967; and another by Cawood and Howell, was published in the International Journal of Oral and Maxillofacial Surgery in 1991, are included as reference.
One can construe from these studies that for a time period as short as several months, the highest point of bone anatomy is toward the lingual side of extracted teeth after healing with considerably more remodeling/resorption on the buccal aspect. Due to the natural bony contours in the anterior area of the upper jaw, this healing pattern, often referred to as facial collapse of bone, is more immediate there than in the posterior upper and lower jawbones.
In the 1980's one of the most commonly placed implant designs was the Branemark type dental implant. As with most traditionally designed implants, and a number today, the Branemark type fixture relied on a flat to flat matting surface perpendicular to the long axis of the implant body as the mating interface when joining the implant and the abutment together. This design usually displays a bone loss pattern described as a cupping of the bone at the coronal end of the implant usually down to the first major thread on the implant body. This bone loss pattern usually stabilizes after about one year of function with vertical bone loss of approximately 1.5 to 2.0 mm.
There are dental implants systems that typically do not demonstrate a cupping bone loss pattern. Two such implant systems are by Astra Tech and Ankylos. Both of these implants have an internal female conical connection and do not rely on flat to flat mating surfaces at the implant/abutment interface. However, the Ankylos surgical protocol suggests placing the implant two millimeters below the crest of bone because the philosophy is to allow bone to grow over the top of the implant and cover at least part of the platform at the coronal aspect of the fixture which extends outward from the abutment conical connection penetration. The Astra protocol is to place the implant at bone level or very slightly below and have the bone integrate apically from the most apical aspect of the reverse bevel at the coronal aspect of the Astra Tech Profile fixture.
Astra Tech now offers implants with a sloping coronal contour such that the height of lingual bone crest is engaged and preserved in sloped ridge situations. In particular, U.S. Pat. No. 7,270,542, to Cottrell, incorporated herein by reference, is directed to such a modified sloped top dental implant fixture. Dental implants made to these design specifications make it easier for surgeons to place implants ideally and maintain the bony topography after healing remodeling has occurred. This modified sloped top dental implant is commercially available as the Astra Tech Profile, and is generally illustrated by FIG. 1 herein.
The Astra Tech system mentioned above has essentially been modified to develop a dental implant with a sloping coronal contour that is convex when viewed in FIG. 1. Much of the success of this implant is credited with Astra Tech design having a combination of a rigid conical abutment connection and the presence of coronal stress reducing micro threads on the implant body which in combination greatly reduce, and in most cases, eliminate the aforementioned bone loss patterns. The reverse bevel at the top of the implant inherent in the design of fixtures with a deep conical connection may also be important as well. It has been proposed, and possibly validated by Degidi in the International Journal of Periodontics and Restorative Dentistry 2012 June: 32(3):323-8, and by Degidi in the Clinical Oral Implant Res. 19, 2008, 276-282 that the circular connective tissue fibers at the base of the implant gingival complex, that develop above the implant once the final abutment is installed, may help prevent apical soft tissue migration acting as a mechanical support mechanism. Both Degidi references are hereby incorporated by reference herein. The Ankylos design has bone growing over the platform at the top of the implant but must be placed deeper below the level of the most apical crestal bone available in order for bone to grow over the top of the fixture. The Ankylos implant has more of a coronal shoulder than Astra's reverse bevel in order to maintain adequate wall thickness for the Ankylos approximate six (6) degree internal conical connection but the shoulder essentially has the same effect with regard to the circular connective tissue fibers. The present disadvantage is that in many instances one side of the implant platform which is, as mentioned above, relatively flat has to be buried deeper than necessary for this overgrowth of bone to occur. This is particularly true in the upper anterior region of the mouth where the Ankylos fixture must be significantly buried on the lingual aspect due to the presenting anatomy in that region, see FIG. 7 herein.
However, while the sloped top implant works very well with extraction sites that have been allowed to heal, and the implant placed following the delayed protocol, it may not be the ideal design when implanted immediately following tooth extraction. Certainly sloped top fixtures work better than traditional flat topped fixtures in the upper anterior region of the mouth, but the contours are still not exactly ideal for immediate placement. In order to compensate for the mismatch between the extraction socket topography and the sloped top design, Cottrell has applied for a patent (application Ser. No. 12/494,510) on a design that has a modified coronal contour. This design calls for the mesial length to be greatest and the buccal length shortest with the lingual and distal dimensions intermediate in length. Viewed from the mesial aspect the coronal contour is convex, as is the contour of the Profile fixture in FIG. 1 as referenced above. The contours of the asymmetric fixture do not perfectly mimic the CEJ contours of the upper anterior teeth because implants are undersized relative to the extraction socket following the immediate placement protocol and as a result some remodeling is going to occur. While the design takes into consideration the height of the lingual side of extraction socket in the upper anterior region it does not follow the contours of the interproximal bone levels which are even higher. The Asymmetric Design, as it is called, tries to anticipate the bone remodeling upon healing remodeling and still preserve some of the interproximal bone height. Unfortunately, while the Asymmetric implant design is ideal in approach it does present a problem. Being asymmetric in character, different fixtures are required for the upper right and upper left anterior regions in the mouth and different fixtures for the upper/lower right and upper/lower left quadrants of the mouth. Consequently, there is concern that potential surgical and inventory complications could arise for the surgeon.
At the coronal aspect of a dental implant placed immediately in the upper anterior region of the mouth a gap is generally present on the mesial, distal and buccal sides on the fixture as only the apical end is firmly anchored in bone and the lingual side ideally but not always in contact with the bone. Accordingly, as mentioned before some remodeling is going to take place as these gaps fill in with new bone. The objective of the asymmetric concept was to design the coronal contour of the dental implant that anticipates how this will occur when immediate implant placement protocol is undertaken. A compromise must be established between the bony contours that exist around the coronal contour of the extraction socket and the contours of the asymmetrical dental implant which best takes into account the angulation that the implant must follow in the extraction socket while anticipating the remodeling process compared to the delayed implant placement protocol.
However this particular improvement caused issues because different fixtures would be required in the upper anterior for the upper right and left sides of the mouth and for the upper left/lower right and upper right/lower left quadrants of the mouth. Additionally, Astra Tech was recently purchased by Dentsply International, who already owns the Ankylos system. As mentioned above, the recommended Ankylos protocol is to bury the implant. So the general object of the present invention is to offer a grand compromise. If Ankylos suggests burying the top of the implant 2.0 millimeters below the lowest level of the available bone, the present disclosure is suggesting there is a way to contour the top of the fixture to prevent burying aspects of the Ankylos shoulder deeper than Ankylos presently recommends, especially on the lingual aspect in the upper anterior region of the mouth. Further the present disclosure would satisfy Astra Tech and others main objection since only one implant design for upper right and left sides of the mouth and all posterior quadrants would be required. Also, since Ankylos buries the top of the fixture having the implant slightly longer on the mesial than the distal isn't as important. While it is more of an issue for a bone level design like Astra Tech's in reality many surgeons bury those fixtures to a degree as well, so being perfectly coronally contoured as the asymmetric design suggest maybe isn't as important for bone level designs as Astra Tech's either. Accordingly, what is being disclosed is a smooth, continuously contoured coronal profile without abrupt change in direction such that the longest mesial and distal lengths are equal, the buccal lengths are shorter than their most adjacent mesial and distal lengths and the lingual lengths are shorter than their most adjacent mesial and distal lengths such that the shortest lingual length is longer than the shortest buccal length. Further, when viewed from the mesial or distal, the outer bone engaging aspect of the coronal contour of the outer aspect of the implant fixture is convex. It is also proposed that in the most ideal configuration that all corresponding mesial and distal lengths, corresponding lingual lengths as well as corresponding buccal lengths are equal. In this case, the meaning of corresponding would be the same lengths in a mirror image reflection such that if the implant were sectioned in the middle buccal to lingual both sides would be identical but a mirror image of one another. The body of the implant can be a tapered or straight walled fixture. Going forward this contour will be referred to as the Ridge Lap design as the coronal contour mimics the underside of a ridge lap pontic in a bridge prosthesis. Anyone skilled in the art will appreciate that as long as the mesial and distal greatest lengths are equal that they do not necessarily have to be correspondingly equal as herein defined. The same would be true for the buccal and lingual lengths as corresponding lengths could be slightly unequal. However, this would result in asymmetry and void one objective of the Ridge Lap concept but done in a way that is not detectable clinically. In other words, the mesial half and the distal half of the coronal contours being mirror images of one another. The proposed Ridge Lap coronal contour, while not as ideal as the Asymmetric Design, will still help overcome the challenge of preserving at least some of the interproximal bone height and allow Ankylos surgeons to reduce the depth of fixture placement, particularly on the lingual aspect as shown in FIG. 8, but still allowing bone overgrowth onto the shoulder of the fixture. The Ridge Lap design allows the top of either the Astra Tech or Ankylos type implant design to better follow the surrounding bony contours in the upper anterior region of the mouth in particular at the time of extraction and still be easy for the surgeons to place clinically.
Interestingly, the Ridge Lap contour also has application for single stage implants as well. Straumann is now the largest implant company in the world and at least 50% of their sales are single stage implants only introducing a bone level fixture into the marketplace in the past 3-4 years. Single stage implants with a level coronal platform do work reasonably well in the upper posterior region of the mouth but require extremely accurate placement by the surgeon. Since the bone and soft tissue in the upper posterior is often flat, the top of the single stage implant works well to provide a margin for the final prosthesis. However, in the lower posterior, the anatomy more often than not shows buccal bone remodeling and the level of the bone and soft tissue on the buccal aspect is more apical. The Ridge Lap contour gets its name by following the underside of a ridge lap pontic of a fixed bridge prosthesis. Contouring the top of a single stage implant to follow the same contour would overcome some of the issues that single stage implants present in the lower posterior. Namely they are often buried deeper than desirable so the top of the implant is not exposed on the buccal aspect. This buries the lingual side of the implant and it can be at times difficult to remove the final luting cement. In years past, cement contamination down the side of the implant was overlooked but recently that has become a hot topic of discussion. Numerous clinicians have presented cases showing bone loss in implant cases where cement has been found to be a contaminant. This has been one of the reasons custom abutments of bone level implants have become so popular since the margin for the final prosthesis is machined to follow only slightly below the soft tissue contours. Therefore, the Ridge Lap contour as applied to a single stage implant as shown in FIG. 10 is considered to be very desirable.
Accordingly, it is the general object of the present Disclosure to provide an implant with a coronal contour that will do much of what Cottrell's Asymmetric Design would accomplish while simplifying the design to have equal mesial and distal contours.
It is a further object of the present disclosure to overcome the challenge of maintaining at least some of the interproximal bone height that has to date been difficult to maintain.
It is another object of the present disclosure to provide a modified dental implant design combining the elements that are known to work in overcoming crestal bone loss such that the problems related to immediate implant placement with respect to maintaining the natural bony topography present at the time of tooth extraction can at least be partially accomplished.
It is a more specific object of the present disclosure to enable single state implants to be placed in a delayed manner in healed sites that exhibit buccal bony remodeling requiring that the buccal aspect of the implant to be placed more apically to follow the soft tissue topography without burying the lingual aspect of the implant.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.